Silver halide emulsions containing cyanine and merocyanine dyes having a 4-pyrazole nucleus

ABSTRACT

Silver halide emulsions are provided which feature certain cyanine and merocyanine dyes containing a 4-pyrazole nucleus.

United States Patent I Continuation-impart of application Ser. No. 604,146, Dec. 23, 1966, now abandoned.

SILVER IIALIDE EMULSIONS CONTAINING CYANINE AND MEROCYANINE DYES HAVING A 4-PYRAZOLE NUCLEUS 41 Claims, No Drawings u.s. c1 96/101, 96/102, 96/135 96/107, 260/240, 260/240.1

BT1 151 (I! .IILIIII G03c 175 6, G030 l/28, C09b 23/00 [50] Field of Search 96/102, 84, l35,l07, l0l;260/240, 240.1

[56] References Cited UNITED STATES PATENTS 2,184,013 l2/l939 Leermakers 96/94 X 2,493,747 [/1950 Brooker et al. 96/84 X 3,379,533 4/l968 Jenkins et al. 96/102 Primary Examiner-Norman G. Torchin Assistant Exam iner-Richard E. Fichter Attorneys-Ogden H. Webster, J. R. Frederick and W. H. J.

Kline ABSTRACT: Silver halide emulsions are provided which feature certain cyanine and merocyanine dyes containing a 4- pyrazole nucleus.

SILVER HALIDE EMULSIONS CONTAINING CYANINE AND MEROCYANINE DYES HAVING A 4-PYRAZOLE NUCLEUS This application is a continuation-in-part of my copending U.S. application Ser. No. 604,146 filed Dec. 23, 1966.

This invention relates to novel photographic materials. In one aspect, this invention is directed to novel photographic silver halide emulsions containing certain cyanine and merocyanine dyes having a 4-pyrazole nucleus, and to photographic elements prepared with such emulsions.

It is known that direct positive images can be obtained with certain types of photographic silver halide emulsions. For example, photographic emulsions have been proposed for this purpose comprising an electron acceptor and silver halide grains that have been fogged with a combination of a reducing agent and a compound of a metal more electropositive than silver. One of the advantages of such direct positive emulsions is that the highlight areas of the images obtained with these materials are substantially free from fog. However, known materials of this type have not exhibited the high speed required for many applications of photography. Also, such known materials have not shown the desired selective sensitivity, especially to radiation in the green to red region of the spectrum. It is evident, therefore, that there is need in the art for improved direct positive photographic materials having both good speed and desirable sensitivity to longer wavelength radiations.

1 have now found that certain cyanine and merocyanine dyes containing certain pyrazole nuclei are outstanding electron acceptors and spectral sensitizers in direct positive type photographic silver halide emulsions. They provide superior reversal systems, especially with fogged silver halide emulsions that are characterized by both good speed and desired sensitivity to radiation in the green to red region of the spectrum, with maximum sensitivity occuring in most cases in the region of about 460550 m. The images produced with these new direct positive photographic emulsions are clear and sharp.

It is, accordingly, an object of this invention to provide new and improved direct positive photographic silver halide emulsions, and more particularly fogged emulsions of this type, containing one or more of the cyanine or merocyanine dyes of .the invention. Another object of this invention is to provide novel light-sensitive photographic elements comprising a support material having thereon at least one layer of the novel direct positive photographic emulsions of this invention. Other objects will become apparent from this disclosure and the appended claims.

In accordance with the invention, novel and improved photographic silver halide emulsions are prepared by incorporating one or more of the cyanine or merocyanine dyes of the invention therein. The emulsion can be a direct positive emulsion, such as a fogged silver halide emulsion. The emulsion can be fogged in any suitable manner, such as by light or with chemical fogging agents, e.g., stannous chloride, formaldehyde, thiourea dioxide and the like. The emulsion may be fogged by the addition thereto of a reducing agent such as thiourea dioxide and a compound of a metal more electropositive than silver such as a gold salt, for example, potassium chloroaurate, as described in British Pat. No. 723,019 (1955 Typical reducing agents that are useful in providing such emulsions include stannous salts, e.g., stannous chloride, hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts such as tetra (hydroxymethyl) phosphonium chloride, and the like. Typical useful metal compounds that are more electropositive than silver include gold, rhodium, platinum, palladium, iridium, etc., preferably in the form of soluble salts thereof, e.g., potassium chloroaurate, auric chloride, (Ni-l ,PdCl, and the like.

Useful concentrations of reducing agent and metal compound (e.g., metal salt) can be varied over a considerable range. As a general guideline, good results are obtained using about 0.05 to 40 mg. reducing agent per mole of sliver halide,

and 0.5 to 15.0 mg. metal compound per mole of sliver halide. Best results are obtained at lower concentration levels of both reducing agent and metal compound.

The concentration of added dye can vary widely, e.g., from about 50 to 2000 mg. and preferably from about 400 to 800 mg. per mole of sliver halide in the direct positive emulsions.

As used herein, and in the appended claims, fogged" refers to emulsions containing silver halide grains which produce a density of at least 0.5 when developed, without exposure, for 5 minutes at 68 F. in developer Kodak DK-SO having the composition set forth below, when the emulsion is coated at a silver coverage of 50 mg. to 500 mg. per square foot.

DEVELOPER N-Methyl-p-aminophenol sulfate 2.5 g. Sodium sulfite (anhydrous) 30.0 g. Hydroquinone 2.5 g. Sodium metaborate 10.0 8. Potassium bromide 0.5 g.

Water to make The dyes of this invention are also advantageously incorporated in direct positive emulsions of the type in which a silver halide grain has a water-insoluble silver salt center and an outer shell composed of a fogged water-insoluble silver salt that develops to silver without exposure. The dyes of the invention are incorporated, preferably, in the outer shell of such emulsions. These emulsions can be prepared in various ways, such as those described in Berriman U.S. Pat. No. 3,367,778 issued Feb. 6, 1968. For example, the shell of the grains in such emulsions may be prepared by precipitating over the core grains a light-sensitive water-insoluble silver salt that can be fogged and which fog is removableby bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is sufficiently fogged to produce a density of at least about 0.5 when developed for 6 minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of mg. per square foot. Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core emulsion, high intensity light and the like fogging means well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged. Fogging by means of a reduction sensitizer, a nobel metal salt such as gold salt plus a reduction sensitizer, a sulfur sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell portion of the subject grains can also be coated prior to fogging.

DEVELOPER A N-Methyl-p-arninophenol sulfate 2.5 g. Ascorbic acid 10.0 g. Potassium metaborate 35.0 g. Potassium bromide 1.0 Water to 1 liter pH of 9.6

Before the shell of water-insoluble silver salt is added to the silver salt core, the core emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can beobtained by various techniques as described herein. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Saubeneir in Science et Industries Photographiques, Vol. XXVIll, Jan. 1957, pages 1 to 23 and Jan. 1957, pages 57 to 65 are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitization, e.g., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

The dyes of this invention are highly useful electron acceptors in high speed direct positive emulsions comprising fogged silver halide grains and a compound which accepts electrons. The fogged silver halide grains of such emulsions are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about one upon processing for 6 minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 1 L49 g. potassium bromide ll9 mg. water to l liter The grains of such emulsions will lose at least about 25% and generally at least-about 40% of their fog when bleached for 10 minutes at 68 F. in a potassium cyanide bleach composition as described herein. This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer and comparing the density of such a coating with an identical coating which is processed for 6 minutes at 68 F. in Kodak DK-5 developer after being bleached for aboutlO minutes at 68 F. in the potassium cyanide bleach composition. As already indicated, the maximum density of the unbleached coating will be at least 30% greater, generally at least 60% greater, than the maximum density of the bleached coating.

The silver halides employed in the preparation of the photographic emulsions useful herein include any of the photographic silver halides as exemplified by sliver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromide, and the like. Silver halide grains having an average grain size less than about 1 micron, preferably less than about 0.5 micron, give particularly good results. The silver halide grains can be regular and can be any suitable shape such as cubic or octahedral. Such grains advantageously have a rather uniform diameter frequency distribution. For example, at least 95%, by weight, of the photographic silver halide grains can have a diameter which is within about 40%, preferably within about 30% of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photoraphic Journal, Vol. LXXlX, 1949, pages 330-338. The fogged silver halide grains in these direct-positive photographic emulsions of this invention produce a density of at least 0.5 when developed without exposure for minutes at 68 F. in Kodak DK-SO developer when such an emulsion is coated at a coverage of 50 to about 500 mg. of silver per square foot of support. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most'preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes, reducing agents and metal compounds of the invention are advantageously incorporated in the washed, finished silver halide emulsion and should, of course, be uniformly distributed throughout the emulsion. The methods of incorporating dyes and other addenda in emulsions are relatively simple and well known to those skilled in the art of emulsion making. For example, it is convenient to add them from solutions in appropriate solvents, in which case the solvent selected should be completely free from any deleterious effect on the ultimate light-sensitive materials. Methanol, isopropanol, pyridine, water, etc., alone or in admixtures, have proven satisfactory as solvents for this purpose. The type of silver halide emulsions that can be sensitized with the new dyes include any of those prepared with hydrophilic colloids that are known to be satisfactory for dispersing silver halides, for example, emulsions comprising natural materials such as gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. and hydrophilic synthetic resins such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate, and the like.

The dyes, reducing agents and metal compounds of the invention can be used with emulsions prepared, as indicated above, with any of the light-sensitive silver halide salts including silver chloride, silver bromide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, etc. Particularly useful for direct positive fogged emulsions in which the silver salt is a silver bromohalide comprising more than 50 mole percent bromide. As indicated previously, certain dyes of this invention are also useful in emulsions which contain color formers. This is unexpected since related prior art dyes cannot be used in emulsions containing a color former.

The novel emulsions of this invention may be coated on any suitable photographic support, such as glass, film base such as cellulose acetate, cellulose acetate butyrate, polyesters such as polyethylene terephthalate, paper. baryta coated paper. polyolefin coated paper, e.g., polyethylene or polypropylene coated paper, which may be electron bombarded to promote emulsion adhesion, to produce the novel photographic elements of the invention.

The cyanine and merocyanine dyes that are useful in practicing the invention include those comprising a pyrazole nucleus, joined, through the four-carbon atom thereof, to a methine linkage; and a second nitrogen heterocyclic nucleus joined through a carbon atom thereof to said methine linkage to complete a cyanine or merocyanine dye. Preferably the said second heterocyclic nucleus is composed of from five to six atoms in the heterocyclic ring, at least one of said atoms being a nitrogen atom, and can be either a sensitizing nucleus or a desensitizing nucleus depending on what sensitizing characteristics are desired in the resulting cyanine dye compound. The cyanine and merocyanine dyes employed herein contain a 4-pyrazolyl nucleus.

One highly useful class of dyes that are especially useful as electron acceptors and spectral sensitizers in the invention are the cyanine and merocyanine dyes represented by the following general formulas:

thiazolidinedione nucleus, e.g., 2,4-thiazolidinedione, 3-ethyl- 2,4-thiazolidinedione, 3-phenyl-2,4-thiazolidinedione, 3-anaphthyl-2,4-thiazolidinedione, etc.; a thiazolidinone nucleus, e.g., 4-thiazolidinone,3-ethyl-4-thiazolidinone, 3-phenyl-4- thiazolidinone, 3-a-naphthyl-4-thiazolidinone, etc.; a 2- thiazolin-4-one nucleus, e.g., 2-ethylmercapto-2-thiazolin-4- one, 2-alkylphenylamino-2-thiazolin-4-one, Z-diphenylamino- 2-thiazolin-4-one, etc.; a 2-imino-4-oxazolidinone (i.e., pseudohydantoin) nucleus; a 2,4-imidazolidinedione (hydantoin) nucleus, e.g., 2,4-imidazolidinedione, 3-ethyl-2,4- imidazolidinedione, 3-phenyl-2,4-imidazolidinedione, 3-anaphthyl-2,4-imidazolidinedione, l,3-diethyl-2,4- imidazolidinedione, 1-ethyl-3-phenyl-2,4-imidazolidinedione, l-ethyl-3etc.; -naphthyl-2,4-imidazolidinedione, 1,3-diphenyl- 2,4-imidazolidinedione, etc.; a 2-thio-2,4-imidazolidinedione (i.e., 2-thiohydantoin) nucleus, e.g., 2-thio-2,4- imidazolidinedione, 3-ethyl-2-thio-2,4-imidazolidinedione, 3- (4-sulfobutyl)-2-thio-2,4-imidazolidinedione, 3-(2-carboxyethyl)-2-thio-2,4-imidazolidinedione, 3-phenyl-2-thio-2,4- imidazolidinedione, 3-a-naphthyl- 2-thio-2,4- imidazolidinedione, l,3-diethyl-2-thio-2,4- imidazolidinedione, l-ethyl-3-phenyl-2-thio-2,4- im idazolidinedione, l-ethyl-3-a-naphthyl-2-thio-2,4- imidazolidinedione, l,3-diphenyl-2-thio-2,4- imidazolidinedione, etc., a 2-imidazolin5-one nucleus, e.g., 2- propylmercapto-Z-imidazolin-S-one, etc.; (especially useful are nuclei wherein Q represents a heterocyclic nucleus containing five atoms in the heterocyclic ring, three of said atoms being carbon atoms, one of said atoms being a nitrogen atom, and one of said atoms being selected from the group consisting of a nitrogen atom, an oxygen atom, and a sulfur atom). The nuclei wherein Z in above formula I represents the atoms necessary to complete a desensitizing nucleus such as a nitro substituted heterocyclic nucleus form particularly efficacious desensitizing dyes and are a preferred dye species for preparing the direct positive photographic emulsions and elements of the invention.

The above-defined cyanine and merocyaninc dyes are in most cases powerful desensitizers for preparing direct positive photographic silver halide emulsions. They are also useful desensitizers for negative type of photographic emulsions. In addition, they are also useful desensitizers emulsions used in the process described in Stewart and Reeves, US. Pat. No. 3,240,618, issued May 10, 1966. It should be further noted that all of the dyes of formulas l and H above absorb light sharply and their colors are uniform and deep, thus making them further useful as filter and backing dyes for photographic layers.

As used herein and in the appended claims, desensitizing nucleus" refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to a gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 0.2 grams dye per mole of silver, cause by electron trapping at least about an 80% loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D-l9 at room temperature. Advantageously, the desensitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described, essentially completely desensitize the test emulsion to blue radiation (i.e., cause a loss of more than about 90 to 95% loss of speed to blue radiation).

The cyanine dyes of formula I are prepared conveniently by heating a mixture of (l) a heterocyclic quaternary salt compound of the formula:

III- z wherein m, R,, X and Z are as previously defined, and (2 a pyrazole compound of the formula:

wherein n, L, R R and R are as previously defined in approximately equimolar proportions, in the presence of a condensing agent, if desired, such as anhydrous sodium acetate, a trialkylamine such as triethylamine, etc., piperidine, N-alkylpiperdines, etc., in an inert solvent medium such as ethanol, acetic anhydride, etc. The crude dyes are then separated from the reaction mixtures and purified by one or more recrystallizations from appropriate solvents, e.g., ethanol.

The merocyanine dyes of formula ii are prepared advantageously by heating a mixture of a compound of above formula IV with a compound of the formula:

.wherein Q is as previously defined, in approximately EXAMPLE I 3-Ethyl-2-[( l-phenyl-4-pyrazolyl)vinyljbenzothiazolium toluenesulfonate H C-N-CsHs 0367117 gHs A mixture of 1.75 g. (lmol.) of l-ethyl-2-methylbenzothiazolium p-toluenesulfonate, 0.86 g. (lmol.) -methylbenzothiazolium l-phenyl-4-pyrazole carboxaldehyde, 1.2 g. (1 mol. +200% excess) of anhydrous sodium acetate and I0 ml. of ethyl alcohol was refluxed 1 hour. After adding ml. of water and chilling, a red tar and a few yellow crystals were separated from the liquid by filtration. The tar and crystals were dissolved in chloroform and chromatographed on alumina. The proper dye was eluted with a mixture of 5 ml. ethyl alcohol and ml. chloroform. A yield of 0.4 g. (16%) of bright yellow crystals were isolated from the eluate, m.p. 232233 C., decomposes. This dye was found to be primarily useful as a filter dye in photographic filter layers.

EXAMPLE 2 2-[ 3 ,S-Dimethyll -phenyl-4-pyrazolyl)vinyl]-3-ethylbenzothiazolium iodide A mixture of 1.5 g. (lmol.) of 3-ethyl-2-me t hylbenzothiazolium iodide, lg. (1mol.) of 3,5-dimethyl-l-phenyl- 4-pyrazole carboxaldehyde, 1.2 g. (1 mol. +200% excess) of anhydrous sodium acetate, and ml. of ethyl alcohol was refluxed 1 hour. After adding 100 ml. of water and chilling, a reddish tar was separated from the supernatant liquid by decantation. The tar was treated with 100 ml. of chloroform and chilled. The crude dye was collected on a filter and washed with chloroform. The dye was purified by recrystallization from methyl alcohol. A yield of 0.9 g. (38%) of pure dye was obtained as bright yellow crystals, m.p. 225-226 C., dec. Anal. Calcd. for C H lN S: l, 26.05.

Found: 1,263 The above prepared dye, containing the sensitizing benzothiazolium nucleus, was tested by the exact procedure described in example 4 below. The results as shown in table 1 hereinafter indicate that this dye is a moderately good electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions.

EXAMPLE 3 3-Ethyl-2-[( 1,3,5 -trimethyl-4-pyrazolyl )vinyl]benzothiazolium iodide A mixture of 1.5 g. (1 mol.) of 3-ethyl-2-methylbenzothiazolium iodide, 1.2 g. (1 mol. +70% excess) of 1,3,5- trimethyl-2-pyrazole carboxaldehyde, 1.2 g. (l mol. +200% excess) of anhydrous sodium acetate, and 10 ml. of ethyl alcohol was refluxed 1 hour. The reaction mixture was chilled and the crude dye collected on a filter and washed with water. After recrystallization from methyl alcohol, 0.8 g. (40%) of pure dye was obtained as dull yellow crystals, m.p. 240-241 C., dec.

Anal. Calcd. for c rr ims; l, 29.85

Found: I, 29.6 The above prepared dye also contains a sensitizing benzothiazolium salt nucleus and when photographically tested in the manner described in example 4 below gave generally similar results as found for example 2, i.e., it qualifies as a moderately good electron acceptor and spectral sensitizer.

EXAMPLE 4 2-{[1-(2-Benzothiazolyl)-3,5-dimethyl-4-pyrazolyl]vinyl} -3- ethylbenzothiazolium iodide A mixture of 1.5 g. (1 mol.) of 3-ethyl-2-methylbenzothiazolium iodide, 1.3 g. (1 mol.) of l-(2- benzothiazolyl)-3,5-dimethyl-4-pyrazole carboxaldehyde, 1.2 g. (1 mol. +200% excess) of anhydrous sodium acetate, and 10 ml. of ethyl alcohol was refluxed 1 hour. The reaction mixture was chilled, and the crude dye was collected on a filter and washed with water. After recrystallization from methyl alcohol, 0.4 g. of pure dye was obtained as tan crystals, m-.p. 271-272 C., dec. This dye likewise contains a sensitizing benzothiazolium salt nucleus, but differs from those of the preceding examples by including a 2-benzothiazolyl substituent in the l-position of the pyrazole nucleus. This dye was photographically tested by the following procedure:

A gelatin silver bromoiodide emulsion (2.5 mole percent of the halide being iodide) and having an average grain size of about 0.2 micron is prepared by adding an aqueous solution of potassium bromide and potassium iodide, and an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin solution of a temperature of 70 C., over a ,period of about 35 minutes. Theemulsion is chill-set,

shredded and washed by leaching with cold water in the conventional manner. The emulsion is reduction-gold fogged by first adding 0.2 mg. of thiourea dioxide per mole of silver and heating for 60 minutes at 65 C. and then adding 4.0 mg. of potassium chloroaurate per mole of silver and heating for 60 minutes at 65 C.

The above prepared dye, 2- [l-(2-benzothiazolyl)- 3,5- dimethyl-4-pyrazolyl]viny1 -3-ethylbenzothiazolium iodide is then added to the above fogged emulsion in amount sufficient to give a concentration of 0.350 grams of the dye per mole of silver. The resulting emulsion is then coated on a cellulose acetate film support at a coverage of mg. of silver and 400 mg. ofgelatin per square foot ofsupport.

A sample of the coated support is then exposed on an Eastman lb sensitometer using a tungsten light source and processed for 6 minutes at room temperature in Kodak D-19 developer which has the following composition:

N-Methyl-p-aminophenol sulfate 2.0 g. Sodium sulfite (anhydrous) 90.0 g. Hydroquinone 8.0 g. Sodium Carbonate (monohydrale 52.5 g. Potassium bromide 5.0 g. Water to make 1.0 liter then fixed, washed and dried. The results are listed in table 1 hereinafter. Referring thereto, it will be seen that the dye of this example has a maximum density in the unexposed areas of 1.74 and a minimum density in exposed areas of 0.04, a maximum sensitivity of 468 my, and a relative speed of 380. This result indicates that the dye compound of the above example is especially well suited to function as both an electron acceptor and spectral sensitizer. It thus provides excellent quality direct positive photographic silver halide emulsions. Excellent magenta images are obtained when the color former l-(2,4,6- trichlorophenyl)-3,3'-(2",4-di-t-amylphenoxyacetamido)benzimidazo-S-pyrazolene is incorporated in the emulsion of this example, the emulsion is coated on a support, exposed to a tungsten source through Wratten filter No. 61 and No. 16, and reversal processed as described in Graham et al. U.S. Pat. 3,046,129, issued July 24, 1962, in example (a) C01. 27, lines 27 et seq. except that black-and-white (MQ) development is omitted, the color development is reduced to 1 minute and is conducted in total darkness until after fixing.

In place of the 3-ethyl-2-methylbenzothiazolium ptoluenesulfonate in the above example, there can be substituted an equivalent amount of 3-ethyl-2-methylbenzoxazolium quaternary salt, e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate,etc. salt, or 3-ethyl-2-methylbenzoselenazolium quaternary salt, e.g., the chloride bromide, iodide, perchlorate, p-toluenesulfonate, etc. salt, to give the corresponding cyanine dyes having generally similar properties as electron acceptors and spectral sensitizers for fogged direct positive photographic silver halide emulsions.

EXAMPLE 5 l,3,3-Trimethyl-2-[( l-phenyl-4-pyrazolyl)vinyl]-3H-indolium iodide sensitizer for fogged direct positive photographic A mixture of 1.5 g. (1 mol.) of 1,2,3,3-tetramethyl-3l-l-indolium iodide, 0.86 g. (1 mol.) of 1-phenyl-4-pyrazole carboxaldehyde, l.2 g. (1 mol. +200% excess) of anhydrous sodium acetate, and ml. of ethyl alcohol was refluxed for 1 hour. The reaction mixture was chilled and the crude dye was collected on a filter and washed first with ethyl alcohol and then with water. After recrystallization from methyl alcohol, 1.7 g. (74%) of pure dye was obtained as orange plates, m.p. 246-247 C., dec.

Anal. Calc'd. for C H lN 1, 27.89.

Found: 1, 27.9

The above prepared dye, containing a sensitizing indolium salt nucleus was photographically tested by the exact procedure of example 4. The results are listed in table 1 and indicate that this dye is a moderately good electron acceptor and spectral silver halide emulsions.

EXAMPLE 6 2- l-( 2-Benzothiazolyl)-3 ,5-dimethyl-4pyrazolyl ]vinyl} 1,2,3-trimethyl-3H-indolium iodide A mixture of 1.5 g. (1 mol.) of l,2,3,3-tetramethyl-3l-l-indolium iodide, 1.3 g. (1 mol.) of l-(2-benzothiazolyl)-3,5- dimethyl-4-pyrazo1e carboxaldehyde, l g. (1 mol. +l50% excess) of anhydrous sodium acetate, and 10 m1. of ethyl alcohol was refluxed 1 hour. The reaction mixture was chilled and the crude dye collected on a filter and washed with water. After recrystallization from methyl alcohol, 0.55 g. of pure dye was obtained as tan plates, m.p. 276277 C. dec. The above prepared dye compound was photographically tested by the exact procedure of example 4. The results shown in table 1 indicate that this dye has excellent relative speed and is a good electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions.

EXAMPLE 7 5,6-Dichloro-2-[ 3,5-dimethyll -phenyl-4-pyrazolyl )vinyl]- l,3-diethylbenzimidazolium iodide A mixture of 1.9 g. (1 mol.) of 5,6-dichloro-1,3-diethyl-2- methyl benzimidazolium iodide, l g. (1 mol.) of 2,5-dimethyll-phenyl-4-pyrazole carboxaldehyde, 10 ml. of ethyl alcohol, and 0.5 ml. of piperidine was refluxed for l and hours. The reaction mixture was chilled and crude dye collected on a filter and washed with ethyl alcohol. After recrystallization from methyl alcohol, 1.1 g. (39%) of pure dye was obtained as pale yellow crystals, m.p. 242243. C., dec. Anal. Calcd. for C J-l Clby2lN l, 22.39

Found: 1, 22.6

EXAMPLE 8 6-Dimethyamino-2-[ 3 ,S-dimethyl- 1 -phenyl-4-pyrazolyl )vinyl l -methylquinolinium iodide N- l C-N-CsH CH3 1 L CH=CH--C N A mixture of 1.6 g. (1 mol.) .of 6-dimethylamino-lmethylquinaldinium iodide, l g. (1 mol.) of 3,5-dimethyl-lphenyl-4-pyrazo1e carboxaldehyde, 10 ml. of ethyl alcohol and 0.5 ml. of piperidine was refluxed 2 hours. The reaction mixture was chilled, and the crude dye was collected on a filter and washed with acetone and then washed with hot water. After recrystallization from methyl alcohol, 1.1 g. (43%) of pure dye was obtained as brownish-orange crystals, m.p. 253-254 C., dec.

Anal. Calcd. for C H IN C, 58.80; H, 5.34; l, 24.88

Found: C, 58.6; H, 5.2; I, 24.9

EXAMPLE 9 6-Dimethylamin0-l-methyl-2-[(1-pheny1-4-pyrazolyl)vinyl] quinolinium iodide A mixture of 1.7 g. (1 mol.) of 6-dimethylaminol methylquinaldinium iodide, 0.9 g. (1 mol.) of l-phenyl-4- pyrazole carboxaldehyde, 10 ml. of ethyl alcohol, and 0.5 ml. or piperidine was refluxed 4 hours. The reaction mixture was chilled and the crude dye collected on a filter and washed with hot water. After recrystallization from methyl alcohol, 1.3 g. (55%) of pure dye was obtained as fine orange needles, m.p. 267268 C., dec.

Anal. Calcd. for C l-1 m l, 26.33

Found: 1, 26.1

The above prepared dyes of examples 7, 8 and 9 were found to be primarily useful as filter dyes in filter or backing layers in photographic elements.

EXAMPLE l0 2- {[1-(2-Benzothiazolyl)-3,5-dimethyl-4-pyrazolyl]vinyll-1- cthylquinolinium iodide.

A mixture of 1.5 g. (1 mol.) of l-ethylquinaldinium iodide, 1.3 g. (1 mol.) of 1-(2-benzothiazolyl)-3,5-dimethyl-4- pyrazole carboxaldehyde, 10 ml. of ethyl alcohol, and 3 drops of piperidine was refluxed 1 hour. The reaction mixture was cooled and treated with 30 ml. of water. The crude dye was collected on a filter and washed with water. After recrystallization from methyl alcohol, 0.1 g. (4%) of pure dye was obtained as dull yellow crystals, m.p. 277278 C., dec.

This dye was photographically tested by the exact procedure of example 4 and found to be an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions as shown in table I.

EXAMPLE 1 1 1 ,3-Diallyl-2-[( 3,5-dimethyl-l-pheny1-4-pyrazolyl)vinyl]imidazo[4,5-b1quinoxalinium iodide CH =CHCH Ill 2 9 N (541-05115 CCH=CH C\ r/ I- C 1 CH3 GE E E:

A mixture of 2.2 g. (1 mol.) of l,3-diallyl-2-methylimidaz0[ 4,5-b]quinoxalinium p-toluenesulfonate, 1.1 g. (1 mol. excess) of 3,5-dimethyl-l-phenyl-4-pyrazole carboxaldehyde, and ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture was chilled and treated with 100 ml. of ether. The oily layer was separated from the supernatant llquid by decantation and then washed with ether. The oily layer was dissolved in acetone and treated with an aqueous solution of sodium iodide. After chilling, the crude dye was collected on a filter and washed with water and than acetone. After recrystallization from methyl alcohol, 1.1 g. (38%) of pure dye was obtained as yellow crystals, m.p. 202-203 C., dec.

Anal. CAlcd. for C H IN l, 22.10

Found: 1, 22.0 The above prepared dye, containing the desensitizing 1,3-diallylimidazo[4,5-b]quinoxalinium salt nucleus, was tested by the exact procedure of example 4 and found to be an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions as shown in table I.

EXAMPLE l2 2-[ 3 ,S-Dimethyll -phenyl-4-pyrazolyl)vinyl ]-1 ,3- diethylimidazo[4,5-b]quinoxalinium iodide CzH 1 CH3 T CCH=CH-C 1- 1= A mixture of 2.1 g. (1 mol.) of 1,3-diethyl-2- rnethylimidazo[4,5-b1quinoxalinium p-toluenesulfonate, 1.1 g. (1 mol. +10% excess) of 3,5-dimethyl-l-phenyl-4-pyrazole carboxaldehyde, and 15 ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture was chilled and treated with ether. The oily layer was separated from the supernatant liquid by decantation and then washed with ether. The oily layer was dissolved in acetone and treated with an aqueous solution of sodium iodide. After chilling, the crude dye was collected on a filter and washed with water and then with acetone. After recrystallization from ethyl alcohol, 0.45 g. (16%) of pure dye was obtained as yellow needles, m.p. 237-238 C., dec.

As tested by the procedure of example 4 and as shown in table 1, this dye is a moderately good electron acceptor and spectral sensitizer for fogged photographic silver halide reversal systems.

. EXAMPLE 13 6-Chloro-2-[(3,5-dimethyl-1-phenyl-4-pyrazolyl)viny1]-l ,3- diphenylimidazo[4,5-b1quinoxalinium p-toluenesulfonate A mixture of 2.7 g. (1 mol.) of 6-ch1oro-2-methyl-1,3- diphenylimidazo[4,5]quinoxalinium p-toluenesulfonate, 1.1 g. (1 mol. +10% excess) of 3,5-dimethyl-l-phenyl-4- pyrazolecarboxaldehyde, and 10 ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture was chilled and then treated with ml. of ether. The oily layer was separated from the supernatant liquid by decantation, and then washed with ether, whereupon it became crystalline. The crude dye was collected on a filter and washed with ether. After recrystallization from ethyl alcohol, 1.6 g. (42%) of pure dye was obtained as small bright yellow crystals, m.p. 28328 4C., dec.

Anal. Calc'd. for C,,,H CLN O;,S: C, 67.88; H, 4.59

Found: C, 68.0; H, 4.7.

The above prepared dye, containing the desensitizing nucleus 6-chloro-l,3-diphenylimidazo[4,5-b1quinoxalinium salt nucleus is an excellent electron acceptor and spectral sensitizer for fogged photographic silver halide reversal systems as indicated by the test procedure of example 4 and as shown by the results listed in table I hereinafter.

EXAMPLE 14 2-[(3,5-Dimethyl-l-phenyl-4-pyrazolyl)vinyl]-l ,S-diphenylimidazol4,5b]quinoxalinium iodide A mixture of 2.6 g. (1 mol.) of 2-methyl-l,3-diphenylimidazo[4,5-b]quinoxalinium p-toluenesulfonate, 1.1 g. (1 mol. +10% excess) of 3,5-dimethyl-1-phenyl-4-pyrazole carboxaldehyde, and 15 ml. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled and treated with 100 ml. of ether. The oily layer was separated from the supernatant liquid by decantation and then washed with ether. The oily layer was dissolved in acetone and treated with an aqueous solution of sodium iodide. After chilling, the crude dye was collected on a filter and washed with water and then acetone, After recrystallization from methyl alcohol, 1.5 g. (47%) of pure dye wasobtained as yellow crystals, m.p. 312-320 C.,dec.

EXAMPLE 15 1,3-Diallyl-2l[1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl] -vinyl imidazol4,5-b]quinoxalinium p-toluenesulfonate A mixture of 4.4 g. (1 mol.) of 1,3-diallyl-2-methylimidazol4,5-b1quinoxalinium p-toluenesulfonate, 2.6 g. (1 mol.) of 1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazole carboxaldehyde, and 30 ml. of acetic anhydride was refluxed 20 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from ethyl alcohol, 1.7 g. (25%) of pure dye was obtained as amber crystals, m.p. 219-220 C., dec.

EXAMPLE 16 I 1 ,3-Diallyl-6-chloro-2-[ 3 ,5-dimethyl-1-pheny1-4- pyrazolyl)vinyl]imidazoe[4,5-blquinoxalinium p-toluenesulfonate A mixture of 2.35 g. (1 mol.) of 1,3-diallyl-6-chloro-2- methylimidazo[4,5-blquinoxalinium p-toluenesulfonate, 1 g. (1 mol.) of 3,5-dimethyl-l-phenyl-4-pyrazole carboxaldehyde, and ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture was chilled, and the crude dye collected on a filter and washed with acetone. After recrystallization from ethyl alcohol, 1.25 g. (37%) of pure dye was obtained as yellow crystals m.p. l89l90 C., dec.

EXAMPLE l7 1,3-Diallyl-6-chloro-2-[(1,3,5-trimethyl-4-pyrazolyl)vinyl]imidazo[4,5-b]quinoxalinium p-toluenesulfonate A mixture of 2.3 g. (1 mol.) of 1,3-diallyl-6-chloro-2- methylimidazo[4,5-b]quinoxalinium p-toluenesulfonate, 0.75 g. (1 mol.) of l,3,5-tnmethyl-4-pyrazole carboxaldehyde, and 10 ml. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled and treated with 100 ml. of ether. The crude dye was collected on a filter and washed with ether. After recrystallization from ethyl alcohol, 1.7 g. (57%) of pure dye was obtained as yellow-orange crystals, m.p. 122-l24 C., dec.

It will be noted that each of the dyes of examples l4, 15, 16 and 17 contains the densitizing imidazo[4,5-b]-quinoxalinium salt nucleus, and that these on photographic testing by the procedure of example 4, as shown in table 1, are indicated as being moderately good to excellent electron acceptors and spectral sensitizers. Accordingly, they are well suited for use in fogged direct positive photographic silver halide emulsions. In this connection, it will be further noted that the dye of example l5 also contains a 2-benzothiazolyl group on the l-position of the pyrazole nucleus and that it shows a marked increase in relative speed and much lower minimum density in the exposed areas, as compared with the dyes of examples 14, 16 and 17.

EXAMPLE 18 2-[ 3 ,S-Dimethyl- 1 -phenyl-4-pyrazolyl )vinyl l-3-ethyl-6- nitrobenzothiazolium p-toluenesulfonate I a C 115 OSOgC HT A mixture of 4 g. (1 mol.) of 3-ethyl-2-methyl-6- nitrobenzothiazolium p-toluenesulfonate, 2 g. 1 mol.) of 3,5- dimethyl-l-phenyl-4-pyrazole carboxaldehyde, and 20 ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture was chilled and then treated with ml. of ether. The oily layer was separated from the supernatant liquid by decantation and washed with ether and then treated with acetone and chilled. The crude dye was collected on a filter and washed with acetone. After recrystallization from ethyl alcohol, 4.5 g. (79%) of pure dye was obtained as brownish yellow needles, m.p. 202-204 C., dec.

Anal. Calcd. for C,,,H N,O S C, 60.39; H, 4.89

Found: C, 60.1; H, 4.7

This dye contains the desensitizing 6-nitrobenzothiazolium salt nucleus and as indicated by the test procedure of example 4, and as shown by the results in table I, it is an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions.

In place of the 3-ethyl-2-rnethyl-6-nitrobenzothiazolium ptoluenesulfonate in the above example, there can be substituted an equivalent amount of other intermediates such as 3-ethyl-2-methyl-6-nitrobenzoxazolium quaternary salt, e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts, or 3-ethyl-2-methyl--nitrobenzoselenazolium quaternary salt, e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts, and the like, to give the corresponding cyanine dyes having generally similar electron acceptor and spectral sensitizer properties, for example, the dye 2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl)vinyl]-3-ethyl- -nitrobenzoxazolium p-toluenesulfonate, the dye 2-[(3,5- dimethyl-l -phenyl-4-pyrazolyl )vinyl]-3-ethyl-6- nitrobenzoselenazolium p-toluenesulfonate, etc. The 3,5-

-dimethyl-l-phenyl-4-pyrazole curboxaldehyde can also be substituted in the above example by an equivalent amount of other related aldehydes such as 3,5-dimethyl-l-phenyl-4- pyrazole acrylaldehyde to give the corresponding cyanine dye 2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl)butadienyl1-3-ethyl-6- nitrobenzothiazolium p-toluenesulfonate having generally similar properties as an electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions.

EXAMPLE 19 A mixture of 1.8 g. (1 mol.) of l,3,3-trimethyl-2-methylene- 1,2-dihydro-3H-pyrrolo[2,3-blpyridine, 2 g. (1 mol.) of 3,5- dimethyl-l-pheny1-4-pyrazole carboxaldehyde, 2.1 g. (1 mol.) of p-toluenesulfonic acid, and 10 ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture was chilled and then treated with 100 ml. of ether. The oily layer was separated from the supernatant liquid by decantation, and washed with ether. The oily layer was dissolved in acetone and treated with an aqueous solution of sodium iodide. After chilling, the crude dye was collected on a filter and washed with water and then with acetone. After recrystallization from ethyl alcohol, 1.4 g. (29%) of pure dye was obtained as orange plates, m.p. 233235 C., dec.

Anal. Calcd. for C I-1 1M; C, 57.01; H, 5.20; I, 26.21

Found: C, 57.3; H, 5.4;], 26.4.

The above prepared dye, containing the desensitizing 3H- pyrrolo[2,3-b]pyridinium salt nucleus, was tested by the exact procedure of example 4 and found to be an excellent electron acceptor and spectral sen'si't'izer for fogged type photographic reversal systems. The results are shown in table I hereinafter.

EXAMPLE 20 2-[ 3 ,S-Dimethyli -phenyl-4-pyrazolyl)vinyl]-l ,3,3- trimethyl-S-nitro-3l-l-indolium p-toluenesulfonate CH CH;

A mixture of 2.4 g. (l mol.) of l,2,3,3-tetramethyl-5-nitro-3 H-indolium p-toluenesulfonate, 1.25 g. (1 mol.) of 3,5- dimethyl-l-phenyl-4-pyrazole carboxaldehyde, and ml. of acetic anhydride was refluxed for 10 minutes. The reaction mixture as chilled and the crude dye collected on a filter, washed with acetic anhydride and then with acetone. After recrystallization from ethyl alcohol, l g. (28%) of pure dye was obtained as yellow crystals, m.p. 21 822l C., dec.

Anal. Calcd. for C ,H N O,S: C, 64.99; H, 5.64

Found: C, 64.7; H, 5.5.

EXAMPLE 2] 5-Chloro-2-[ 3,5-dimethyll -phenyl-4-pyrazolyl )vinyl]-3- ethyl-6-nitrobenzothiazolium iodide C Ns A mixture of 3.9 g. (1 mol.) of 5-chloro-3-ethyl-2-methyl-6-; nitrobenzothiazolium iodide, 2 g. (l mol.) of 3,5-dimethyl-l-f phenyl-4-pyrazole carboxaldehyde, and ml. of acetic an-;

hydride was refluxed 10 minutes. The reaction mixture was} chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 2.2 g.;

(38%) of pure dye was obtained as brownish needles, m.p.i

229 230 C., dec. 9

Anal. Calcd. for C,,H, CllN.,O,S: C, 46.59; H, 3.56; l, 22.39

Found: C, 46.4; H, 3.3; 1, 22.5.

EXAMPLE 22 2-[(3,5-Dimethyll -phenyl-4-pyrazolyl)vinyl1-3- ethylthiazolo[4,5-blquinolinium chloride EXAMPLE 23 I 2-[(3,5-Dimethyll -phenyl-4pyrazolyl)vinyll-b nitroquinolinium iodide C 3115 (all l-ethyl-6- A mixture of 3.4 g. (1 mol.) of l-ethyl-6-nitroquinaldinium iodide, 2 g. (1 mol.) of 3.5-dimethyl-l-phenyl-4-pyrazole carboxaldehyde, and 15 ml. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled and treated with ml. of ether. The oily layer was separated from the supernatant liquid by decantation and then treated with ethyl alcohol. The crude dye was extracted with 450 ml. of methyl alcohol. The filtrate was concentrated to 25 ml. and chilled, and the dye collected on a filter. After recrystallization from methyl alcohol, 0.2 g. (4%) of pure dye was obtained as brownish crystals, m.p. l28-l 3 1 C., dec.

Photographic testing in accordance with the procedure of example 4 indicated that above prepared dye, containing the desensitizing 6-nitroquinolinium salt nucleus, is a moderately good electron acceptor and spectral sensitizer for fogged type photographic reversal systems.

- EXAMPLE 24 l,3-Diallyl-2-[( l-phenyl-4-pyrazolyl)vinyl]imidazo[4,5-b

. ]quin oxalinium p-toluei iesulfonate A mixture of 4.4 g. (1 mol.) of l,3-diallyl-2-methylimidazo[ 4,5-b1quinoxalinium p-toluenesulfonate, l.7 g. (1 mol.) of lphenyl-4-pyrazole carboxaldehyde, and 10 ml. of acetic anhydride was refluxed l0 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 3.2 g. (54%) of pure dye was obtained as brownish crystals, m.p. 232-233 C., dec.

EXAMPLE 25 l6-Chlorol ,3-diphenyl-2-[( l-phenyl-4-pyrazolyl)vinyl1imidazo-[4,5 -blquinoxalinium p-toluenesulfonate A mixture of 5.4 g. (l mol.) of 6-chloro-l,3-diphenyl-2- methylimidazo[4,5-b]quinoxalinium p-toluenesulfonate, 1.7 g. (1 mol.) of l-phenyl-4-pyrazole carboxaldehyde, and ml. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 3.4 g. (49%) of pure dye was obtained as yellowish plates, m.p. 29l-292C., dec.

The dyes of above examples 24 and 25, each containing a desensitizing l,3-diallylimidazo[4,5-b]quinoxalinium salt nucleus, were tested by the exact procedure of example 4 and found, as shown in table 1 hereinafter, to be relatively good electron acceptors and spectral sensitizers for fogged direct positive photographic silver halide emulsions. The dye of example 24 showed the best relative speed, of 603 as compared to 263 for the dye of example 25, but in all other properties both dyes were about the same.

EXAMPLE 26 3-Ethyl-6-nitro-2-[( l-phenyl-4-pyrazolyl)vinyl]benzothiazolium p-toluenesulfonate A mixture of 4 g. (1 mol.) of l-ethyl-2-methyl-6- nitrobenzothiazolium p-toluenesulfonate, 1.7 g. (1 mol.) of lphenyl-4-pyrazole carboxaldehyde, and ml. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 3.9 g. (71%) of pure dye was obtained as orange crystals, m.p. 276-277 C., dec.

EXAMPLE 27 3-Ethyl-6-nitro-2-[( l ,3,5-trimethyl-4-pyrazolyl)vinyllbenzoth iazolium p-toluenesulfonate A mixture of 4 g. (1 mol.) of 3-ethyl-2-methyl-6 nitrobenzothiazolium p-toluenesulfonate, 1.4 g. (1 mol.) of l,3,5-trimethyl-4-pyrazole carboxaldehyde, and 15 ml. of acetic anhydride was refluxed l0 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 3.5 g. (69%) of pure dye was obtained as brown needles, m.p. 253-254 C., dec.

EXAMPLE 28 l ,3-Diallyl-2{ l-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl] -vinyl}-6-chloroimidazo[4,5-b]quinoxalinium p-toluenesulfonate A mixture of 4.7 g. (1 mol.) of l,3-diallyl-6-chloro-2- methylimidazo[4,5-b]quinoxalinium p-toluenesulfonate, 2.6 g. (1 mol.) of l-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazole carboxaldehyde, and 20 ml. of acetic anhydride was refluxed 15 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 1.6 g. (22%) of pure dye was obtained as yellow crystals, m.p. 23023 1 C., dec.

EXAMPLE 29 2 [l-( 2-Benzothiazolyl)-3,5-dimethyl-4-pyrazolyl]vinyl -3- ethyl-6-nitrobenzothiazolium p-toluenesulfonate A mixture of 4 g. (1 mol.) of 3-ethyl-2-methyl-6- nitrobenzothiazolium p-toluenesulfonate, 2.6 g. (l mol.) of l- (2-benzothiazolyl)-3,5-dimethyl-4-pyrazole carboxaldehyde, and 20 ml. of acetic anhydride was refluxed l5 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone. After recrystallization from methyl alcohol, 0.95 g. (l5%) of pure dye was obtained as brown needles, mp 249250 C., dec.

The above prepared dyes of examples 26, 27 and 29 containing the desensitizing 6-nitrobenzothiazolium salt nucleus, and the dye of example 28 containing the desensitizing imidazo-[4,5-b]quinoxalinium salt nucleus, were tested by the procedure of example 4, and found, as shown in table I hereinafter, to be moderately good to excellent electron acceptors and spectral sensitizers for fogged direct positive photographic silver halide emulsions, differing from one another primarily in relative speeds as indicated in table I.

In place of the 3-ethyl-2-methyl-6-nitrobenzothiazolium ptoluenesulfonate in above example 29, there can be substituted an equivalent amount of other intermediates such as a 3-alkyl-2-methyl-6-nitrobenzoxazolium quaternary salt, e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salt, or a 3-all yl-2-methyl-6-nitrobenzoselenazolium quaternary salt, e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salt, and the like intermediates, to give the corresponding cyanine dyes having generally similar electron acceptor and spectral sensitizer properties, for example, the dye 2-l[l-(2-benzothiazolyl)-3,5- dimethyl-4-pyrazolyllvinyl -3-ethyl-6-nitrobenzoxazolium ptoluenesulfonate, the dye 2-}[l-(2-benzothiazolyl)-3,5- dimethyl-4-pyrazolyl]vinyl }-3-ethyl-6-nitrobenzoselenazolium p-toluenesulfonate, etc.

EXAMPLE 30 2-[(3,5-Dimethyll -phenyl-4-pyrazolyl)vinyl]-3- methylthiazolinium' iodide I CH:

A mixture of 2.5 g. (1 mol.) of 2,3-dimethy1thiazolinium iodide, 2 g. (1 mol.) of 3,5-dimethyl-1-phenyl-4-pyrazole carboxaldehyde, and 10 ml. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled and the crude dye collected on a filter and washed with acetone After recrystallization from ethyl alcohol, 1.4 g. (33%) of pure dye was obtained as brownish needles, m.p. 249250 C., dec.

The above prepared dye, containing a sensitizing thiazolinium salt nucleus, was tested in accordance with the procedure of example 4 and found, as shown in table 1 hereinafter to be a useful electron acceptor and spectral sensitizer for fogged type photographic reversal systems.

EXAMPLE 31 3-Methyll -phenyl-4-[( 1-phenyl-4-pyrazolyl)methylene]-2- pyrazoline-S-one A mixture of 1.7 g. (1 mol.) of 3-methyl-1-phenyl-2- pyrazolin-5-one, 1.7 g. (l mol.) of l-phenyl-4-pyrazole carboxaldehyde, and ml. of acetic acid were heated at 100 C. for 1 hour. The reaction mixture was chilled and the crude dye collected on a filter and washed with ether. After recrystallization from benzene 2.2 g. (67%) of pure dye was obtained as yellow needles, m.p. l76-178C., dec.

Anal. Calc'd. for C,,,H, N O: C, 73.15; H, 4.92

Found: C, 73.2; H, 5.1

EXAMPLE 32 3-Ethyl-5-[( l-phenyl-4-pyrazolyl)methylene]rhodanine A mixture of 1.6 g. (1 mol.) br 3-ethylrhodanine, 1.7 g. (1 mol.) of l-phenyl-4-pyrazole carboxaldehyde, and 10 ml. of acetic acid were heated at 100 C. for 2 hours. The reaction mixture was chilled and the crude dye was collected on a filter and washed with ether. After recrystallization from benzene, 0.4 g. (13%) of pure dye was obtained as yellow plates, m.p. 230-232d.

Anal. Calc'd. for C H N OS C, 57.1 1; H, 4.16

Found: C, 57.4; H; 3.9.

EXAMPLE 33 4-[(3,5-Dimethyl-1 -phenyl-4-pyrazo1yl)methylenel-1 ,2- diphenyl-3 ,S-pyrazolidinedione A mixture of 1.3 g. (1 mol.) of 1,2-diphenyl-3,5- pyrazolidinedione, 1 g. (1 mol.) of 3,5-dimethyl-1-phenyl-4- pyrazole carboxaldehyde, and 10 ml. of acetic acid was heated at C. for 1 hour. The reaction mixture was treated with water and the oil was separated by decantation. The oil was treated with ethyl alcohol and the crude dye was collected on a filter. After crystallization from benzene, 0.1 g. (4%) of pure dye was obtained as yellow crystals, m.p. 1 7 1 C., dec.

EXAMPLE 34 3-Ethyl-5-[( l,3,5-trimethyl-4-pyrazolyl)methylene ]rhodanine A mixture of 1.6 g. (1 mol.) of 3-ethy1rhodanine, 1.4 g. (1 mol.) of 1,3,5-trimethy1-4-pyrazole carboxaldehyde, and 10 ml. of acetic acid was refluxed for 1 hour. The reaction mixture was chilled and the crude dye collected on a filter and washed with ether. After recrystallization from benzene, 0.45 g. (16%) of pure dye was obtained as yellow needles, m.p. l56-158 C., dec.

Anal. Calcd. for C, H, N OS C, 51.21; H, 5.38.

Found: C, 51.2; H, 5.4.

EXAMPLE 35 4-[ 3,5-Dimethyll -phenyl-4-.pyrazolyl)methylene] 3-pheny1- 2-isoxazolin-5-one A mixture of 3.2 g. (1 mol.) of 3-phenyl-2-isoxazolin-5-one, 4 g. (1 mol.) of 3,5-dimethyl-1-phenyl-4-pyrazole carboxaldehyde, and 20 m1. of acetic anhydride was refluxed 10 minutes. The reaction mixture was chilled, and the crude dye collected on a filter and washed with ether. After recrystallization from a 50-50 mixture of benzene and petroleum ether, 4.2 g. (61%) of pure dye was obtained as bright yellow crystals, m.p. 162164C.

The above prepared dyes of examples 31 to 35 were photographically tested in accordance with the procedure of example 4 and found to be useful as electron acceptors and spectral sensitizers for photographic reversal systems. For example, the most useful dye of this group was that of example 34.

A number of the above prepared dye compounds were photographically tested by the exact procedure described in example 4. The results as shown in table 1 immediately below, indicate that many of the dyes listed in the table areerninently suitable for preparing the novel and improved, fogged direct positive photographic silver halide emulsions and new photographic elements of the invention.

TABLE I Densih Dye con- Sensicentration, Relative Maximum Minimum tizmg Ex. g./mo1e White light in unexposed in exposed max No. silver clear speed areas areas (m Dyes having an unsubstituted pyrazole nucleus can be prepared by reacting methyl hydrazine with malodialdehyde to obtain l-acetylpyrazole, using reaction conditions similar to those in example 37 below; reacting Lacetylpyrazole with phosphoryl chloride and dimethylformamide in dioxane as described in example 39 below to obtain l-acetyl-4-pyrazole carboxaldehyde; reacting l-acetyl-4-pyrazole carboxaldehyde with an intermediate of the type used in cyanine or merocyanine dyes, such as 1,3-diallyl-6-chloro-2- methylimidazo[4,5-b1quinoxalinium p-toluenesulfonate or 3- ethylrhodanine; and, hydrolyzing the acetyl group off the pyrazole nucleus with dilute sodium hydroxide, to obtain, for example, 1,3-diallyl-2-[(4-pyrazolyl)-viny1]-6- chlorobenzimidazo[4,5e-blquinoxalinium p-toluenesulfonate or 3-ethyl-5-[(4-pyrazolyl)methylene]rhodanine. Cyanine and merocyanine dyes having an unsubstituted 4-pyrazolyl nucleus exhibit photographic properties generally similar tosubstituted 4-pyrazole dyes, such as the dyes of examples 1 through 35.

The following examples illustrate the preparation of some of the intermediates employed in the preceding examples to prepare the specified dye compounds.

EXAMPLE 36 1-(2-Benzothiazolyl)-3,5-dimethylpyrazole To a solution of 50 g. (1 mol.) of 2,4-pentanedione in 150 ml. of ethyl alcohol was added 82.5 g. (l mol.) of 2- benzothiazolylhydrazine with shaking. The reaction mixture became warm and solid separated. After the addition was 1 complete, the mixture was refluxed 2 hours. The reaction mixture was chilled and the solid collected on a filter and washed with ethyl alcohol. A yield of 1 14 g. (100%) was obtained. A sample was recrystallized from methyl alcohol for analysis; m.p. 146-147C. Anal. Calcd. for C l-1 ,14 8: C, 62.83; H, 4.84

Found: C, 62.6; H, 5.1

EXAMPLE 37 1 ,3,5-Trimethylpyrazole CHa- I /CH To a solution of 23 g. (1 mol.) of methyl hydrazine in 100 ml. of ethyl alcohol was added 50 g. (1 mol.) of 2,4-pentanedione over a period of 30 minutes with stirring, keeping the temperature below 40 by means of an ice bath. After the addition was complete, the reaction mixture was refluxed 1 hour. The reaction mixture was then fractionated through a column. A yield of 44 g. (80%) of colorless liquid with a b.p.

of 167-168 C. was obtained.

EXAMPLE 38 1-(2-Benzothiazolyl)-3,5-dirnethyl-4-pyrazole carboxaldehyde nn CN-C I c-c110 To a suspension of 64 g. (1 mol.) of l-(2-benzothiazolyl)- 3,5-dimethylpyrazole in 52 ml. of dimethylformimide, was added 33.5 ml. of phosphoryl chloride with shaking. The reaction mixture was heated at 150 for 16 hours, then cooled and suspended in 1500 ml. of water and made alkaline with sodium carbonate. The solid was collected on a filter and washed with water and then extracted with 1500 ml. boiling methyl a1- cohol. After chilling, the methyl alcohol solution filtered and the filtrate diluted with 1 l. of water. The solid which separated was collected on a filter and washed with water. A yield of 22.6 g. (3 1%) of colorless crystals were obtained, m .p. 1 l8-l20 C.

C CHr-II CCHO A solution of 42 g. (1 mol. +10% excess) of phosphoryl chloride in ml. of dioxane was added to a solution of 20 g. (1 mol. +10% excess) of dimethylformamide in 100 ml. of dioxane. Then, a solution of 27.5 g. (1 mol.) of 1,3,5- trimethylpyrazole in 50 ml. of dioxane was added dropwise with stirring. After the addition was complete, the reaction mixture was heated 2 hours on a steam bath. After cooling, a solution of ml. of about 8% sodium hydroxide was added. The reaction mixture was cooled and the solid collected on a filter and then discarded. Solid sodium carbonate was added until effervescence ceased. The reaction mixture separated into three layers and the bottom aqueous layer was discarded. The upper two layers were continuously extracted with ether for 2 hours. The ether extract was concentrated and the residue distilled under reduced pressure. When the temperature of the vapors reached 1 15l15 mm., distillation was stopped and the residue considered good material. A yield of 17.3 g. (50%) of brownish solid was obtained. A sample recrystallized from ethyl alcohol had m.p. 8283 C.

The preparation of fogged, direct positive photographic emulsions and elements with a number of the cyanine dyes of the invention is illustrated by the following examples.

EXAMPLE 40 To 9.0 pounds of a silver chloride gelatin emulsion containing an equivalent of 100 grams of silver nitrate is added 0.017 gram of 1,3-diallyl-2-[(3,5-dimethyl-1-phenyl-4-pyrazolyl)viny1]imidazo[4,5-b]quinoxalinium iodide (example 11). The emulsion is coated'on a nonglossy paper support, and is flashed with white light to give a density of, 1.2 when developed in the following developer, diluted 1 part to 2 parts of water:

N-methyl-p-aminophenol sulfate 3.1 g. Sodium sulfite, des 45 g. Hydroquinone 12 g. Sodium carbonate. des 67.5 g. Potassium bromide 1.9 g. Water to 1 liter The light fogged material can be exposed to an image with light modulate by a Wratten No. 15 filter to give a direct positive image. Similar results are obtained when the dye of example 13 is substituted for the 1,3-diallyl-2-[(3,5-dimethyl-1- phenyl-4-pyrazolyl)vinylimida2o[4,5-b]quinoxalinium iodide.

EXAMPLE 4] Seven pounds of a silver chloride gelatin emulsion containing the equivalent of 100 g. of silver nitrate is heated to 40 C. and the pH is adjusted to 7.8. Eight cc. of full strength (40%) formalin solution is added and the emulsion is held at 40 C. for minutes. At the end of the holding period, the pH is adjusted to 6.0 and 0.125 g. of 2-[(3,5-dimethyl-l-phenyl-4- pyrazolyl)vinyl-3-ethyl-6-nitrobenzothiazolium-ptoluenesu1- fonate (example 18) is added. The emulsion is coated on a support, and provides good direct positive images. Similar results are obtained when the dye of example 20 is substituted for the 2-[(3,5-dimethyl-1-phenyl-4-pyrazolyl)viny1-3-ethyl-6- nitrobenzothiazolium-p-toluenesulfonate.

By substituting other dye compounds of the invention, as defined in formula 1 above, into the procedure of the above examples 40 and 41, and more particularly the dyes of examples 2, 4-6, 10, 12, 14-17, 19 and 21-29, generally similar fogged, direct positive photographic silver halide emulsions and photographic elements may be prepared.

The photographic silver halide emulsion and other layers present in the photographic elements made according to the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxy starch or oxy plant gums, and the like. The emulsion layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain in some cases additional spectral sensitizing dyes. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. Among the useful color formers are the monomeric and polymeric color formers, e.g., pyrazolone color formers, as well as phenolic, heterocyclic and open chain couplers having a reactive methylene group. The color forming couplers can be incorporated into the direct positive photographic silver halide emulsion using any suitable technique, e.g., techniques of the type shown in Jelley et al. U.S. Pat. No. 2,322,027, issued June 15, 1943, Fierke et al. U.S. Pat. No. 2,801,171, issued July 30, 1957, Fisher U.S. Pat. Nos. 1,055,155 and 1,102,028, issued Mar. 4, 1913 and June 30, 1914, respectively, and Wilmanns U.S. Pat. No. 2,186,849 issued Jan. 9, 1940. They can also be developed using incorporated developers such aspolyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Certain novel dyes of this invention are claimed as new compositions of matter in my U.S. Pat. applications Ser. No. 604,161 titled Cyanine Dyes, now U.S. Pat. 3,515,722 and Ser. No. 604,181, titled "Novel Cyanine Dyes, now U.S. Pat. No. 3,542,772 both filed concurrently with the present application.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood thatvariations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and, as defined in the appended claims.

lclaim:

1. A'fogged direct positive photographic silver halide emulsion containing a cyanine or merocyanine dye compound having a pyrazole nucleus joined through the four carbon atom thereof to a methine linkage, and a second nitrogen heterocyclic nucleus of the type used in cyanine and merocyanine dyes joined through a carbon atom thereof to said methine linkage.

2. A direct positive photographic emulsion of claim 1 wherein said methine linkage is a dimethine linkage.

3. A direct positive emulsion of claim 2 wherein said second heterocyclic nucleus contains from five to six atoms in the heterocyclic ring, at least one of said atoms being a nitrogen atom.

4. A direct positive emulsion of claim 1 wherein said second heterocyclic nucleus is selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, a thiazoline nucleus, a pyridine nucleus, a quinoline nucleus, a 3,3-dialkylindolenine nucleus, an imidazole nucleus, an imidazo[4,5-bIquinoxaline nucleus, a 3,3-dialkyl-3H-pyrrolo[ 2,3-b]pyridine nucleus, and a thiazolo[4,5-b]quinoline nucleus.

5. A direct positive emulsion of claim 4 wherein said methine linkage is a dimethine linkage.

6. A direct positive. emulsion of claim 1 wherein said pyrazole nucleus is substituted in the 1-position thereof by a heterocyclic substituent selected from the group consisting of a 2-thiazolyl nucleus, a 2-oxazolyl nucleus, a 2-selenazolyl nucleus, a quinolyl nucleus, a pyridyl nucleus, a 2-indolyl nucleus and a 2-imidazolyl nucleus.

7. A direct positive emulsion of claim 6 wherein said methine linkage is a dimethine linkage.

8. A direct positive emulsion of claim 1 in which the said silver halide is present in the form oflight fogged silver halide grains.

9. A direct positive emulsion of claim 1 in which the said silver halide is present in the form of chemically fogged silver halide grains.

10. A direct positive emulsion of claim 1 containing a photographic color former.

11. A fogged direct positive photographic silver halide emulsion containing a dye selected from those having one of the following formulas:

wherein m and d each represents a positive integer of from l selected from the group consisting of a hydrogen atom, an

alkyl group and an aryl group; Xrepresents an acid anion; R represents a member selected from the group consisting of hydrogen, an alkyl group, an aryl group and the group -,z, -C(=CHCH)N wherein p represents a positive integer of from 1 to 4; Z represents the nonmetallic atoms required to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring selected from the nuclei consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, a thiazoline nucleus, a pyridine nucleus, a quinoline nucleus, a 3,3-dialkylindolenine nucleus and an imidazole nucleus; 2 represents the nonmetallic atoms required to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring selected from the nuclei consisting of a nucleus of 2,, an imidazo[4,5-b]quinoxaline nucleus, a 3,3- dialkyl-3H-pyrrolo[2,3-b1pyridine nucleus and a thiazolo[4,5- bIquinoline nucleus; and, Q represents the nonmetallic atoms required to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring, three to four of said atoms being carbon atoms, one of said atoms being a nitrogen atom, and one of said atoms being selected from the group consisting of a nitrogen atom, an oxygen atom and a sulfur atom.

12. A direct positive emulsion of claim 11 wherein said dye is represented by the formula:

wherein m represents a positive integer of from 1 to 2; n represents a positive integer of from 2 to 3; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; R and R each represents a member selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group; R represents a member selected from the group consisting of hydrogen, an alkyl group, an aryl group and the group wherein p represents a positive integer of from 1 to 4; Z represents the nonmetallic atoms required to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring selected from the nuclei consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, a thiazoline nucleus, a pyridine nucleus, a quinoline nucleus, a 3,3-dialkylindolenine nucleus and an imidazole nucleus; and Z represents the nonmetallic atoms required to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring selected from the nuclei consisting of a nucleus of 2,, an imidazo[4,5-b]-quinoxaline nucleus, a 3,3- dialkyl-3H-pyrrolo[2,3-b]pyridine nucleus and a thiazolo [4,5-b1quinoline nucleus.

13. A direct positive emulsion of claim 12 wherein said n is 2.

14. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a thiazole nucleus.

15. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete an oxazole nucleus.

16. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a selenazole nucleus.

17. A direct positive emulsion of claim 12 wherein said 2 represents the atoms required to complete a thiazoline nucleus.

18. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a pyridine nucleus.

19. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a quinoline nucleus.

20. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a 3,3-dialkylindolenine nucleus.

21. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete an imidazole nucleus.

22. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete an imidazo[4,5-b] quinoxaline nucleus.

23. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a 3,3-dialkyl-3H- pyrrolo[2,3-b]pyridine nucleus.

24. A direct positive emulsion of claim 12 wherein said 2 represents the atoms required to complete a thiazolo[4,5-b] quinoline nucleus.

25. A direct positive emulsion of claim 12 wherein said R represents a substituent selected from the group consisting of a 2-thiazolyl nucleus, a 2-oxazolyl nucleusya 2-selenazole nucleus, a pyridyl nucleus, a quinolyl nucleus, an indolyl nucleus and an imidazolyl nucleus. 1

26. A direction positive emulsion of claim 12 wherein said R represents a Z-benzothiazolyl nucleus.

27. A direct positive emulsion of claim 12 in which said silver halide is present in the form of light fogged silver halide grains.

28. A direct positive emulsion of claim 12 in which said silver halide is present in the form of chemically fogged silver halide grains.

29. A fogged direct positive photographic silver halide emulsion containing a dye selected from the group consisting of a 2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl)vinyl]3-ethylbenzothiazolium salt, a 2-{[ l-(2-benzothiazolyl)-3,5- dimethyl-4-pyrazolyl]vinyl}3-ethylbenzothiazolium salt, a l,3,3-trimethyl-2-[(1-phenyl-4-pyrazolyl)vinyl1-3H-indolium salt, a 2- l-( benzothia'zolyl)-3,5-dimethyl-4-pyrazolyllvinyl} l ,3,3-trimethyl-3H-indolium salt, a 2-{[1-(2-benz0thiazolyl)- 3,5-dimethyI-4-pyrazolyllvinyl}-l-ethylquinolinium salt, a l,3-diallyl-2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl )vinyl]imidazo-[4,5-b]quinoxalinium salt, a 2-[(3,5-dimethyl lphenyl-4-pyrazolyl )vinyl l ,B-diethyl-imidazcl 4,5-b]quinoxalinium salt, a 6-chloro-2-[(3,5-dimethyl-l-phenyl-4- pyrazolyl)vinyl]- l ,3-diphenylimidazo[4,5-b ]quinoxalinium salt, a 2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl)vinyl]-l,3- diphenyl-imidazo[4,5-b1quinoxalinium salt, a l,3-diallyl-2-} [l-( 2-benzothiazolyl)-3,5 -dimethyl-4-pyrazolyl]vinyl} imidazo[4,5-b]quinoxalinium salt, a l,3-diallyl-6-chloro-2- 3 ,5-dim ethyl-4-phenyl-4-pyrazolyl-vinyl] imidazo 4,5- b]quinoxalinium salt, a 1,3-diallyl-6-chloro-2-[(1,3,5- trimethyl-4-pyrazolyl)vinyl]imidazo[4,5-b]quinoxalinium salt, a 2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl)vinyl]-3-ethyl- 5-nitrobenzothiazolium salt, a 2-[(3,5-dimethyl-l-phenyl-4- pyrazolyl )vinyl]- l ,3 ,3-trimethyl-3l-l-pyrrolo[2,3-blpyridinium salt, a 2-[(3,5-dimethyl-l-phenyl-4-pyrazolyl)vinyl]-l,3,3- trimethyl-5-nitro-3H-indolium salt, a 5-chloro-2-[(3,5- dimethyl-1-phenyl-4-pyrazolyl)vinyl]-3-ethyl-6- nitrobenzothiazolium salt, a 2-[(3,5-dimethyl-l-phenyl-4- pyrazolyl)vinyl]-3-ethylthaizolo-[4,5-b]quinolinium salt, a 2- [(3,5-dimethyl- 1 -phenyl-4-pyrazolyl )vinyl]- l -ethyl-6- nitroquinolinium salt, a l,3-diallyl-2-[( l-phenyl-4- pyrazolyl)vinyl]imidazo[4,5-b]quinoxalinium salt, a 6 chlo ro l,3-diphenyl-2-[( l-phenyl-4-pyrazolyl)vinyl] imidazo-[4,5-b] quinoxalinium srlt, a 3-ethyl-6-nitro-2-[( l-phenyl-4- pyrazolyl)vinyllbenzothiazolium salt, a 3-ethyl-6-nitro-2-[( l, 3,5-trimethyl-4-pyrazolyl)vinyl]benzothiazolium salt, a 1,3-diallyl-2 [l-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl]-vinyl }-6-chloroimidazo[4,5-b]quinoxalinium salt, a 2-} l(2- benzothiazolyl )-3 ,5-dimethyl-4-pyrazolyl vinyl }-3-ethyl-6- nitrobenzothiazolium salt, and a 2-[(3,5-dimethyl-l-phenyl-4- pyrazolyl)vinyl]-3-methylthiazolium salt.

30. A direct positive emulsion of claim .29 in which the said silver halide is present in the form of chemically fogged silver halide grains.

31. A direct-positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about l upon processing for 6 minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak Dis-i; developer after being bleached for about minutes at about 68 F. in a bleach composition of:

potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 1 L49 g. potassium bromide H9 mg. water to l liter 32. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

33. A direct positive, photographic emulsion in accordance with claim 12 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-SO developer after being bleached for about 10 minutesat about 68 F. in a bleach composition of:

potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 1 L49 g. potassium bromide ll9 mg. water to l liter 34. A direct positive, photographic emulsion in accordance with claim 11 which comprises fogged silver halide grains, at

H least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

35. A fogged direct positive photographic silver halide emulsion comprising l,3-diallyl-2-[(3,5-dimethyll -phenyl-4- pyrazolyl)vinyl]imidazoe[4,5-b1quinoxalimium salt and fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about l upon processing for 6 minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test Eortion which is processed for 6 minutes at about 68 F. in odak DK-SO developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 11.49 g. potassium bromide 1 l9 mg. water to 1 liter 36. A fogged direct positive photographic silver halide emulsion comprising l,3-diallyl-2-[(3,5-dimethyl-l-phenyl-4- pyrazolyl)vinyllimidazoe[4,5-b]quinoxalinium salt and fogged silver halide grains, at least by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

37. A photographic element comprising a support having coated thereon a direct positive photographic emulsion as defined in claim 1.

38. A photographic silver halide emulsion containing as desensitizer a cyanine or merocyanine dye compound having a pyrazole nucleus joined through the four-carbon atom thereof to a methine linkage, and a second nitrogen heterocyclic nucleus of the type used in cyanine and merocyanine dyes joined through a carbon atom thereof to said methine linkage.

39. An emulsion of claim 38 wherein said second heterocyclic nucleus is selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, at thiazoline nucleus, a pyridine nucleus, a quinoline nucleus, a 3,3-dialkylindolenine nucleus, an imidazole nucleus, an imidazo[4,5-b]quinoxaline nucleus, a 3,3-dialkyl-3H-pyrrolo- [2,3-b1pyridine nucleus, and a thiazolo[4,5-b]quinoline nucleus.

40. An emulsion of claim 38 wherein said pyrazole nucleus is substituted in the l-position thereof by a heterocyclic substituent selected from the group consisting of a 2-thiazolyl nucleus, a 2-oxazolyl nucleus, a 2-selenazolyl nucleus, a quinolyl nucleus, a pyridyl nucleus, a 2-indolyl nucleus and a 2- imidazoly] nucleus.

41. A fogged direct positive photographic emulsion containing a cyanine or merocyanine dye having a 4-pyrazolyl nucleus.

* k i i 

2. A direct positive photographic emulsion of claim 1 wherein said methine linkage is a dimethine linkage.
 3. A direct positive emulsion of claim 2 wherein said second heterocyclic nucleus contains from five to six atoms in the heterocyclic ring, at least one of said atoms being a nitrogen atom.
 4. A direct positive emulsion of claim 1 wherein said second heterocyclic nucleus is selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, a thiazoline nucleus, a pyridine nucleus, a quinoline nucleus, a 3, 3-dialkylindolenine nucleus, an imidazole nucleus, an imidazo( 4, 5-b)quinoxaline nucleus, a 3,3-dialkyl-3H-pyrrolo(2,3-b)pyridine nucleus, and a thiazolo(4,5-b)quinoline nucleus.
 5. A direct positive emulsion of claim 4 wherein said methine linkage is a dimethine linkage.
 6. A direct positive emulsion of claim 1 wherein said pyrazole nucleus is substituted in the 1-position thereof by a heterocyclic substituent selected from the group consisting of a 2-thiazolyl nucleus, a 2-oxazolyl nucleus, a 2-selenazolyl nucleus, a quinolyl nucleus, a pyridyl nucleus, a 2-indolyl nucleus and a 2-imidazolyl nucleus.
 7. A direct positive emulsion of claim 6 wherein said methine linkage is a dimethine linkage.
 8. A direct positive emulsion of claim 1 in which the said silver halide is present in the form of light fogged silver halide grains.
 9. A direct positive emulsion of claim 1 in which the said silver halide is present in the form of chemically fogged silver halide grains.
 10. A direct positive emulsion of claim 1 containing a photographic color former.
 11. A fOgged direct positive photographic silver halide emulsion containing a dye selected from those having one of the following formulas:
 12. A direct positive emulsion of claim 11 wherein said dye is represented by the formula:
 13. A direct positive emulsion of claim 12 wherein said n is
 2. 14. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a thiazole nucleus.
 15. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete an oxazole nucleus.
 16. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a selenazole nucleus.
 17. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a thiazoline nucleus.
 18. A direct positive emulsion of claIm 12 wherein said Z represents the atoms required to complete a pyridine nucleus.
 19. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a quinoline nucleus.
 20. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a 3,3-dialkylindolenine nucleus.
 21. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete an imidazole nucleus.
 22. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete an imidazo( 4,5-b) quinoxaline nucleus.
 23. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a 3,3-dialkyl-3H-pyrrolo(2,3-b)pyridine nucleus.
 24. A direct positive emulsion of claim 12 wherein said Z represents the atoms required to complete a thiazolo( 4,5-b)quinoline nucleus.
 25. A direct positive emulsion of claim 12 wherein said R4 represents a substituent selected from the group consisting of a 2-thiazolyl nucleus, a 2-oxazolyl nucleus, a 2-selenazole nucleus, a pyridyl nucleus, a quinolyl nucleus, an indolyl nucleus and an imidazolyl nucleus.
 26. A direction positive emulsion of claim 12 wherein said R4 represents a 2-benzothiazolyl nucleus.
 27. A direct positive emulsion of claim 12 in which said silver halide is present in the form of light fogged silver halide grains.
 28. A direct positive emulsion of claim 12 in which said silver halide is present in the form of chemically fogged silver halide grains.
 29. A fogged direct positive photographic silver halide emulsion containing a dye selected from the group consisting of a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-ethylbenzothiazolium salt, a 2- (1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl)vinyl 3-ethylbenzothiazolium salt, a 1,3,3-trimethyl-2-((1-phenyl-4-pyrazolyl)vinyl)-3H-indolium salt, a 2- (1-(benzothiazolyl)-3,5-dimethyl-4-pyrazolyl)vinyl -1,3,3-trimethyl-3H-indolium salt, a 2- (1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl)vinyl -1-ethylquinolinium salt, a 1,3-diallyl-2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)imidazo-(4,5 -b)quinoxalinium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-1,3-diethyl-imidazo(4,5 -b)quinoxalinium salt, a 6-chloro-2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-1,3 -diphenylimidazo(4,5-b)quinoxalinium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl) -1,3-diphenyl-imidazo(4,5-b)quinoxalinium salt, a 1,3-diallyl-2- (1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl)vinyl imidazo(4,5-b)quinoxalinium salt, a 1,3-diallyl-6-chloro-2-((3,5-dimethyl-4-phenyl-4-pyrazolyl)-vinyl) imidazo(4,5-b)quinoxalinium salt, a 1, 3-diallyl-6-chloro-2-((1,3,5-trimethyl-4-pyrazolyl)vinyl)imidazo(4,5 -b)quinoxalinium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-ethyl-5-nitrobenzothiazolium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-1,3,3-trimethyl-3H-pyrrolo(2,3 -b)pyridinium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-1,3,3-trimethyl-5-nitro-3H -indolium salt, a 5-chloro-2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-ethyl-6 -nitrobenzothiazolium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-ethylthaizolo-(4,5 -b)quinolinium salt, a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl) -1-ethyl-6-nitroquinolinium salt, a 1,3-diallyl-2-((1-phenyl-4-pyrazolyl)vinyl)imidazo(4,5-b)quinoxalinium salt, a 6-chloro-1,3-diphenyl-2-((1-phenyl-4-pyrazolyl)vinyl)imidazo-(4,5 -b)quinoxalinium salt, a 3-ethyl-6-nitro-2-((1-phenyl-4-pyrazolyl)vinyl)benzothiazolium salt, a 3-ethyl-6-nitro-2-((1, 3, 5-trimethyl-4-pyrazolyl)vinyl)benzothiazolium salt, a 1,3-diallyl-2- (1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl)-vinyl -6-chloroimidazo(4,5-b)quinoxalinium salt, a 2- (1-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl)vinyl -3-ethyl-6-nitrobenzothiazolium salt, and a 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-methylthiazoyinium salt.
 30. A direct positive emulsion of claim 29 in which the said silver halide is present in the form of chemically fogged silver halide grains.
 31. A direct-positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68* F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68* F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68* F. in a bleach composition of: potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 11.49 g. potassium bromide 119 mg. water to 1 liter
 32. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.
 33. A direct positive, photographic emulsion in accordance with claim 12 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68* F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68* F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68* F. in a bleach composition of: potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 11.49 g. potassium bromide 119 mg. water to 1 liter
 34. A direct positive, photographic emulsion in accordance with claim 11 which comprises fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.
 35. A fogged direct positive photographic silver halide emulsion comprising 1,3-diallyl-2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)imidazo(4,5 -b)quinoxalimium salt and fogged silver halide grains, said grains being such that a test portion thereof, when Coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68* F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68* F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68* F. in a bleach composition of: potassium cyanide 50 mg. acetic acid (glacial) 3.47 cc. sodium acetate 11.49 g. potassium bromide 119 mg. water to 1 liter
 36. A fogged direct positive photographic silver halide emulsion comprising 1,3-diallyl-2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)imidazo(4,5 -b)quinoxalinium salt and fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.
 37. A photographic element comprising a support having coated thereon a direct positive photographic emulsion as defined in claim
 1. 38. A photographic silver halide emulsion containing as desensitizer a cyanine or merocyanine dye compound having a pyrazole nucleus joined through the four-carbon atom thereof to a methine linkage, and a second nitrogen heterocyclic nucleus of the type used in cyanine and merocyanine dyes joined through a carbon atom thereof to said methine linkage.
 39. An emulsion of claim 38 wherein said second heterocyclic nucleus is selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, a thiazoline nucleus, a pyridine nucleus, a quinoline nucleus, a 3,3-dialkylindolenine nucleus, an imidazole nucleus, an imidazo(4,5-b)quinoxaline nucleus, a 3,3-dialkyl-3H-pyrrolo-(2,3-b)pyridine nucleus, and a thiazolo(4,5-b)quinoline nucleus.
 40. An emulsion of claim 38 wherein said pyrazole nucleus is substituted in the 1-position thereof by a heterocyclic substituent selected from the group consisting of a 2-thiazolyl nucleus, a 2-oxazolyl nucleus, a 2-selenazolyl nucleus, a quinolyl nucleus, a pyridyl nucleus, a 2-indolyl nucleus and a 2-imidazolyl nucleus.
 41. A fogged direct positive photographic emulsion containing a cyanine or merocyanine dye having a 4-pyrazolyl nucleus. 